1. Field of the Invention
The present invention relates to an aeration-less water treatment apparatus that performs a purifying treatment on waste water such as urban sewage, industrial liquid waste, and household liquid waste using microorganisms.
2. Description of the Related Art
JPA KOKAI Publication No. 11-285696 proposes an aeration-less water treatment apparatus utilizing anaerobic and aerobic microorganisms, as means for performing a purifying treatment on sewage. As shown in FIG. 1, in a conventional apparatus 100, sewage is drivingly introduced into an anaerobic reactor 104 through a line L1 by means of a pump 102. The anaerobic reactor 104 comprises an up flow anaerobic sludge blanket (hereinafter referred to as a “UASB”) section 105 made up of a granular mass of anaerobic microorganisms and a supernatant section 106. Upon passing through the UASB section 105 in the form of an upward flow 107, waste water contacts anaerobic microorganisms in the UASB section 105. Then, organic polluted matter is removed from the sewage. The waste water from which the organic polluted matter has been removed by an anaerobic treatment passes sequentially through the supernatant section 106, an overflow section 108, and a line L2. The waste water is thus fed to the top of an aerobic reactor 110.
The aerobic reactor 110 comprises an aerobic microorganism adhering carrier section 111, a carrier support section 112, and a lower cavity section 113. A diffusion pipe 116 communicating with a blower 114 via an air line 115 is located in the lower cavity section 113. A treatment water reservoir 118 communicates with a side surface portion of the lower cavity section 113 via a line L3. When anaerobic treatment water fed into the aerobic reactor 110 contacts aerobic microorganisms in the aerobic microorganism adhering carrier section 111 while flowing as a down flow, the organic polluted matter remaining in the treatment water from the anaerobic reactor 104 is treated and discharged to the reservoir 118.
However, during a treatment operation performed by the conventional apparatus, various variations and disturbances described below may occur.
(1) Increase in the amount of inflow sewage
(2) Degraded quality of inflow sewage (increase in the amount of organic polluted matter)
(3) Mixture of a toxic substance or the like into the inflow sewage
(4) Increase in the amount of suspended solids in the inflow sewage
(5) Increase in the amount of gas generated
(6) Decrease in the concentration of the inflow sewage (from high-concentration biochemical oxygen demand (BOD) industrial liquid waste to low-concentration BOD sewage)
If any of the variations and disturbances (1) to (6) occurs, then in the conventional apparatus 100, anaerobic microorganisms (UASB) in the anaerobic reactor 104 flow out. This may result in problems (i) to (iii).
(i) Decrease in the concentration of microorganisms in the anaerobic reactor
(ii) Activation of the anaerobic microorganisms in the aerobic reactor
(iii) Degraded quality of treated water
Normally, in the uppermost portion of the UASB section 105, a line velocity Lv associated with the amount of inflow sewage from a pump 102 is balanced with the fall velocity of UASB grains at a fixed height.
However, if (1) the increased amount of inflow of sewage increases the velocity of the upward flow 107 in the anaerobic reactor 104, the uppermost portion of the UASB section shifts upward to disadvantageously cause anaerobic microorganisms to flow out from the anaerobic reactor 104 to the aerobic reactor 110. Normally, the UASB does not flow out at a line velocity Lv of at most about 2 m/h. However, when the line velocity Lv exceeds 2 m/h, the UASB shifts (floats up) toward the top of the anaerobic reactor 104 and flow out from the anaerobic reactor 104 to the aerobic reactor 110.
If (2) the quality of the inflow sewage is degraded or (3) a toxic substance or an inhibitor mixes into the sewage, the limited load value for the UASB in the aerobic reactor 104 is exceeded. Consequently, the UASB may proliferate excessively or be dispersed and reduced and thus have a reduced specific gravity. The reduced specific gravity of the UASB makes the anaerobic microorganisms likely to flow out from the anaerobic reactor 104 to the downstream aerobic reactor 110 as in the case of disturbance (1), described above.
If (4) the amount of suspended solids in the inflow water increases, the shear force and agitating force of the suspended solids shear and crush the UASB, which is a mass (aggregate) of the anaerobic microorganisms. Thus, disadvantageously, the UASB may be dispersed and reduced.
(5) An increase in the anaerobic activity of the UASB causes the anaerobic microorganisms to generate a large amount of methane gas or CO2 gas. The anaerobic microorganisms thus generate fermentation gas. The fermentation gas causes disturbance in the upward flow. The UASB is thus entrained in the fermentation gas and flow out toward the aerobic reactor 110 simultaneously with the upward flow.
(6) The UASB is originally utilized for industrial liquid waste treatment apparatuses containing high-concentration organic polluted matter with a biological oxygen demand (BOD) of several ten thousand to several hundred thousand mg/L. When the UASB is applied to a treatment apparatus containing low-concentration organism polluted matter with a BOD of 100 to 200 mg/L as in the case of sewage, the following problems may occur.
The anaerobic microorganisms constituting UASB are firmly aggregated into a mass by a sticky substance produced at a high-concentration BOD. However, when the anaerobic microorganisms are applied to sewage which has a low-concentration BOD, no sticky substance is produced, and the massive anaerobic microorganisms are dispersed and reduced. When dispersed and reduced, the UASB has a reduced specific gravity and thus floats up to the top of the anaerobic reactor 104 and then flows out from the anaerobic reactor 104.
When (i) the volume of the UASB section 105 in the anaerobic reactor 104 decreases, that is, the concentration of the anaerobic microorganisms decreases as described above, the throughput of the anaerobic reactor is reduced.
Furthermore, (ii) since the UASB is the mass of the anaerobic microorganisms, the UASB flowing out to the aerobic reactor 110, corresponding to the next step, reduces the concentration of dissolved oxygen (DO) in the aerobic reactor 110 to establish an anaerobic environment. Thus, the activity of the aerobic microorganisms in the aerobic reactor 110 is degraded. This reduces not only the treatment performance of the anaerobic reactor 104 but also the treatment performance of the aerobic reactor 110.
(iii) The degraded performance of the reactors 104 and 110 precludes the organic polluted matter in waste water from being sufficiently removed. Consequently, the quality of final treated water is disadvantageously degraded.